键是一种标准件，通常用于联接轴与轴上旋转零件与摆动零件，起周向固定零件的作用以传递旋转运动和扭矩，楔键还可以起单向轴向固定零件。而导键、滑键、花键还可用作轴上移动的导向装置。 根据键的结构形式，键联接可分为平键联接、半圆键联接、楔键联接和切向键联接等几类。

The key is a standard part, which is usually used to connect the rotating parts and swing parts of the shaft and the axle to move the fixed parts to tran***it rotary motion and torque, and the wedge key can also play a one-way axial fixation part. The guide, slippery key and the spline can also be used as a guiding device for moving on the axis. According to the structure of the key, key joins can be divided into a flat bond, a semicircle bond, a wedge bond and a tangent bond.

机用虎钳的结构及原理。机用虎钳是机械加工中常用的装夹机构，其结构如图1所示。其主要工作原理：转动方头带动丝杠，在螺母（通过紧固螺钉固定在虎钳体上）的作用下，做螺旋运动的丝杠带动与之联接的活动座沿丝杠轴线方向来回移动。

The structure and principle of machine vise. Machine vise is a common clamping mechani*** in mechanical processing. Its structure is shown in Figure 1. The main principle: rotation of the lead screw nut in the square, (fixed in the vise body through a fastening screw) under the action of moving spirally driven screw connected with the movable seat to move back and forth along the screw axis.

装夹后产品靠近活动钳口附近容易上翘、抬起，多次装夹一致性差。传统机用虎钳的螺旋副间隙较大，在使用中会产生较大振幅的振动；而活动座和虎钳体之间的滑动接触面较大，采用的间隙也较大。

After the clamping, the product is easy to and lifted near the movable jaw, and the cistency of the clamping is poor many times. The spiral pair clearance of traditional machine vice is bigger, which will cause large amplitude vibration in use. The sliding contact between movable seat and jaw vice body is larger, and the gap used is bigger.